IS 3660 ( Part 12 ) : 1989 Indian Standard ( Reaffirmed 2000 ) METHODSOFTESTFORNATURAL PART 12 DETERMINATION OF PLASTICITY RETENTION RUBBER INDEX (PRI ) [NR: 131 ( First Revision ) UDC 678'4 : 539'214 @I BIS 1990 BUREAU MANAK February 1990 OF BHAVAN, INDIAN STANDARDS ZAFAR MARG Price Group 2 9 BAHADUR SHAH NEW DELHI llOOb2 Rubber Sectional Committee, PCDC 14 FOREWORD This Indian Standar *d ( Part 12 ) ( First Revision ) was adopted by the Bureau of Indian Standards on 14 April 1989, after the draft finalized by the Rubber Sectional Committee had been approved by the Petroleum, Coal and Related Products Division Council. `Methods IS 3660: of test for natural 1 ) : 1972 rubber' had been originally covered in the following four parts of (Part Determination of dirt, volatile matter, ash, total copper, manganese, iron, rubber hydrocarbon, viscosity ( shearing disc viscometer ), and mixing and vulcanizing of rubber in a standard compound (first revision) Determination Plasticity of solvent extract retention and nitrogen content index storage-hardening test and (Part (Part 2 ) : 1968 3,) : 1971 and plasticity ( Part 4 ) : 1979 Determination of colour, vulcanization characteristics accelerated ( MOD test ) While reviewing the various test methods for natural rubber, the Committee decided to align No unification of test methods for natural them with the corresponding International Standards. However, in revising test methods for and synthetic rubber has been considered necessary. natural rubber, the Committee had decided to revise and split the standard ( IS 3660 ) in further parts and publish individual test methods under natural rubber (NR ) series. For proper referencing of the existing test methods and the new methods under revision, a table showing correspondence of various methods of test covered in the previous parts of IS 3660 ( Parts 1, 2, 3 and 4) with the presently split parts vis-a-vis the original NR : number have been given in the Table in Annex A. In order to facilitate cross-reference, it has been decided to retain the original discrete NR series number assigned to various test methods as indicated in original IS 3660 ( Parts 1, 2, 3 and 4) in the new revised Parts of IS 3660. The test method given in this revised standard will supersede the test method as given under All the four parts of the original IS 3660 shall be withdrawn NR: 13 of IS 3660 (Part 3 ) : 1971. upon its complete revision. In the preparation of this standard, assistance has been derived from IS0 2930-1981 `Rubber, raw of plasticity retention index ( PRI )`, published by the International natural - Determination Organization for Standardization ( IS0 ). The plasticity retention index ( PRI ) is a measure of the resistance of raw natural rubber to It is an improvement over earlier tests in that a quantitative, as opposed to a visual, oxidation. assessment of oxidation behaviour is obtained. A high resistance to oxidation is shown as a high value of the index. The oxidation behaviour of raw natural rubber may have an important bearing on processing behaviour and vulcanizate performance, and the PRI test accordingly affords a convenient means of characterizing rubber in some of these respects. In reporting the results of a test or analysis made in accordance with this standard, if the final value, observed or calculated, is to be rounded off, it shall done in accordance with IS 2 : 1960 `Rules for rounding off numerical values ( revised )`. IS 3660 ( Part 12 ) : 1989 Indian Standard METHODSOFTESTFORNATURALRUBBER PART 12 DETERMINATION OF PLASTICITY RETENTiON INDEX ( PRI ) [NR:13] ( First Revision ) 1 SCOPE 1.1 This standard ( Part 12 ) prescribes a method for determination of plasticity retention index ( PRI ) of the raw natural rubber. 2 REFERENCES 2.1 The following Indian Standards sary adjuncts to this standard: IS h-0. 3660 (Part Title 1 ) : 1972 Methods of test for natural rubber : Part 1 Determination of ash, total copper, manganese, rubber hydrocarbon, viscosity ( shearing disc viscometer ), and mixing and vulcanizing of rubber in a standard compound ( jirst revision ) [under revision as 5660 ( Part (NR: 17)] 16 ) are necesabout 4 mm, and operating 20 f 3 kPa. 4.3 Laboratory with a pressure of Mixing Mill The laboratory mixing mill has two parallel and cylindrical hardened-steel rolls 152'5 f 2'5 mm in outside diameter. The rolls are fitted with adjustable guides to allow a maximum working width of 255 f 15 mm. The mill has provision for maintaining the temperature of the roll surfaces at 70 f 5°C during the mixing of the rubber. The two rolls rotate at different speeds. The speed of the slow roll is 24 f 2 rev/min and the friction ratio is 1 : 1'4. a) If the mills having ratios of fast to slow rolls speed lower than 1'4 are used, modifications in the mixing conditions given under procedure may be required to obtain results comparable to those obtained with the standard mill. b) The mill is designed to permit adjustment of the distance between the rolls from 0.2 mm or less to 3'0 mm or more. 4.4 Oven Capable of the following performance at 140°C: 3660 ( Part 11 ) : 1989 Methods of test for natural rubber : Part 11 Determination of plasticity (jint revision ) 3 OUTLINE OF THE METHOD 3.1 Plasticity of natural rubber test pieces before and after heating in an oven for 30'00 f 0'25 minutes at 140°C is measured using parallel plate plastimeter with a platen 10 mm in diameter and following the procedure specified in The PRI IS 3660 (Part II) : 1989 (NR : 12). is then calculated as the percentage ratio of plasticities before and after heating. 4 APPARATUS 4.1 Parallel Plate Plastimeter With a platen 10 mm in diameter, and nunch for preparation of test pieces, as. spec&ed in IS3660(Part11):1989(NR:12). 4.2 a) Control of temperature in the vicinity of the test pieces to be within f 0'2°C over a 30 min period, NOTE -A larger tolerance will impair the accuracy of test. temperature recovery of the b) Allowing oven and the inserted tray and dishes to within 1°C of the set temperature in a time not exceeding two minutes after insertion of the tray in the oven, and c) Changing the air ten times per hour. this perfor- NOTE - Ovens designed to achieve mance are commercially available. Thickness Gauge 4.5 Li .ght Weight Disposable Dishes and Trays Aluminium Having a scale graduated in unit divisions of 0'01 mm, fitted with a flat contact of diameter 1 Suitable dishes have a thickness of 0'2 mm and a diameter of 40 to 50 mm. Any dishes and IS 3660 (Part 12 ) : 1989 correct temperature retained. is quickly regained and trays used shall have low thermal capacity; the total mass of tray and dishes shall not exceed 35 g> and their volume shall not exceed 5 percent of the volume of the oven chamber. 5 PROCEDURE 5.1 Test Piece Homogenize the raw rubber as specified in 3 of IS 3660 ( Part 1 ) : 1972. Take a test portion of about 30 g from the homogenized piece and pass three times ( doubling the sheet between passes) between the rolls of the mill at ambient temperature, running with the nip adjusted so that the final sheet thickness is about 1'7 mm. Immediately double the sheet, which shall be uniform in texture and free from holes, and lightly press the two halves together by hand, avoiding the formation of air bubbles. Cut test pieces as specified in IS 3660 ( Part 11 ) : 1989 (NR : 12 ) from the doubled sheet with the punch and measure their thicknesses with the gauge until six test pieces are obtained with thicknesses between 3.2 and 3'6 mm. Randomly divide these into sets of three, one set each for test before ageing and after ageing. The preparation of test pieces, as described above, shall be carried out with care since the PRI is affected by the sheet thickness. The required nip setting shall be ascertained by a preliminary trial; it may vary with the rubber and with the If six test pieces of the required thickmill. nesses as above are not obtained, a fresh doubled sheet shall be prepared. 5.2 Ageing Before ageing is started, check that the temperature of the oven is remaining at 140'0 f 0'2°C for at least five minutes. The aluminium trays for loading test pieces also may be preheated at this stage. While the trays are kept for preheating in the oven, tissue papers cut to the size of the bottom area of the trays may be kept in them. These papers are kept to prevent sticking of the rubber pieces to the trays while being aged. NOTE-To ensure that all test pieces are aged at the correct temperature, the oven shall not be overloaded. This may cause a severe prolonged drop and may upset temperature uniformity. 5.2.2 After 30'00 f 0'25 min, remove the tray from the oven and the dishes from the tray. Allow them to cool to ambient temperature. 5.3 Determination of Plasticity Carry out the rapid plasticity determination as specified in IS 3660 ( Part 11 ) : 1989 ( NR : 12 ). These determinations shall normally be made at least 0'5 h and not more than 2 h after ageing, with the provison that the test pieces have been allowed to cool to ambient tempePlasticity determinations on unaged rature. and aged test pieces shall preferably be made concurrently. The paper used shall conform to the requirements given in IS 3660 ( Part 11 ) : 1989 ( NR : 12 ) and the rapid plasticity number shall be read to the nearest 0'5 unit. 6 REPORTING OF RESULTS 6.1 The median values for the rapid plasticity numbers of three unaged and three aged test pieces shall be used to calculate the PRI using the formula: Plasticity = retention index ( PRI ) median aged rapid plasticity number x 100 median unaged rapid plasticity number 7 REPEATABILITY 0F RESULTS 7.1 The coefficient of variation V is dependent on the accuracy of the ageing temperature. For PRI calculated as in 6 from the median plasticity values, V is 3 percent when ageing at 140'0 f 0'2°C and f 6 percent at 140 f 1%. Both values of V are consistent with an accuracy of f 3 percent for single determination of rapid plasticity number, 8 TEST REPORT 8.1 The test report shall include particulars: the following 4 Reference to this standard, b) Sample identification including bales, lot and 5.2.1 The aluminium trays may be taken out and loaded with test pieces and quickly inserted back to the oven. Close the oven door and start timing. Care shall be taken to ensure that the dishes and trays are arranged within the calibrated region of the oven. Check that the 4 4 Median rapid plasticity number for unaged and aged test pieces from each sample tested, PRI for each sample tested, and 4 Type of oven used. IS 3660 ( Part 12 ) : 1989 ANNEX A TABLE SHOWING CORRESPONDENCE OF THE VARIOUS METHODS OF TEST COVERED IN THE EXISTING IS 3660 ( PART 1) : 1972, IS 3660 ( PART 2 ) : 1968, IS 3660 ( PART 3 ) : 1971 AND IS 3660 ( PART 4 ) : 1979 WI'IH THE REVISION/ PROPOSED REVISION OF THE FOUR PARTS OF IS 3660 I-_-_-_--__--Test Methods (1) Existing Test Methods h----_-______---~ IS No. (2) Proposed Revision c-------h----_-_-7 ( Series ) IS No. !4) ~(5) Remarks Part ( Series) (3) (6) NR Series Determination Determination Determination Determination Determination Determination of of of of of of dirt volatile matter ash total copper manganese iron IS IS IS IS IS IS 3660 : 1972 3660 : 1972 3660 : 1972 3660 : 1972 3660 : 1972 3660 : 1972 Part Part Part Part Part Part 1 1 1 1 1 1 ( NR ( NR (NR ( NR (NR ( NR : 1) :2) :3) : 4) :5) :6) :7) :8) Determination of rubber hydrocarbon Determination of viscosity by shearing disk viscometer Mixing and vulcanizing in a standard compound Determination of solvent extract Determination of nitrogen content Determination of plasticity Determination of plasticity retention index ( PRI ) Determination of colour Determination of storagehardening test Determination of vulcanization characteristics ( MOD test ) Method for preparation of test samples IS 3660 IS 3660 IS 3660 IS 3660 IS 3660 IS 3660 IS 3660 : 1972 : 1972 : 1972 : 1968 : 1968 : 1971 : 1971 Part 1 (NR Part 1 (NR IS 3660 ( Part 1 ) : 1985 IS3660(Part2):1985 IS 3660 ( Part 3 ) : 1988 IS 3660 ( Part 4 ) : 1988 IS 3660 ( Part 5 ) : 1989 Deleted since this test is no longer being done IS 3660 ( Part 6 ) : 1988 IS 3660 (Part IS3660(Part8): 7) (NR : 1) (NR:2) ( NR : 3 ) (NR : 4 ) ( NR : 5 ) ( NR (NR (NR:9) :7) : 8) 1 : 1988 Part 1 ( NR : 9) Part 2 ( NR Part 2 ( NR Part 3 ( NR Part 3 ( NR Part 4 ( NR Part 4 (NR Part 4 (NR Part : 10 ) : 11 ) : 12 ) : 13 ) : 14) : 15) : 16) ' Under IS 3660 ( Part 9 ) : 1989 ( NR : 10 ) t revision IS 3660 (Part 10) : (NR:ll)J IS 3660 ( Part 11 ) : 1989 (NR IS 3660 (Part 12) : 1989 (NR IS 3660 ( Part IS 3660 ( Part 13 ) 14 ) : 12 ) : 13) 1 IS 3660 : 1979 IS 3660 : 1979 IS 3660 IS 3660 : : : : (NR: 14) (NR:l5) 1 : 1979 : 1972 IS 3660 ( Part 15) IS 3660 ( Part 16 ) ( NR : 16 ) 1 $$z, (NR: v 1 ( Clause 3) I Standard Mark The use of the Standard Mark is governed by the provisions of the Bureau of Indian Standards The Standard Mark on products Act, 1986 and the Rules and Regulations made thereunder. covered by an Indian Standard conveys the assurance that they have been produced to comply with the requirements of that standard under a well defined system of inspection, testing and quality Standard marked control which is devised and supervised by BlS and operated by the producer. products are also continuously checked by BIS for conformity to that standard as a further safeguard. 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